Commit c9b5d98b authored by Ankur Arora's avatar Ankur Arora Committed by Juergen Gross
Browse files

xen/vcpu: Handle xen_vcpu_setup() failure in hotplug 



The hypercall VCPUOP_register_vcpu_info can fail. This failure is
handled by making per_cpu(xen_vcpu, cpu) point to its shared_info
slot and those without one (cpu >= MAX_VIRT_CPUS) be NULL.

For PVH/PVHVM, this is not enough, because we also need to pull
these VCPUs out of circulation.

Fix for PVH/PVHVM: on registration failure in the cpuhp prepare
callback (xen_cpu_up_prepare_hvm()), return an error to the cpuhp
state-machine so it can fail the CPU init.

Fix for PV: the registration happens before smp_init(), so, in the
failure case we clamp setup_max_cpus and limit the number of VCPUs
that smp_init() will bring-up to MAX_VIRT_CPUS.
This is functionally correct but it makes the code a bit simpler
if we get rid of this explicit clamping: for VCPUs that don't have
valid xen_vcpu, fail the CPU init in the cpuhp prepare callback
(xen_cpu_up_prepare_pv()).

Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: default avatarAnkur Arora <ankur.a.arora@oracle.com>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent 0e4d5837

arch/x86/xen/enlighten.c

+26 −20
Original line number Diff line number Diff line
@@ -106,8 +106,10 @@ int xen_cpuhp_setup(int (*cpu_up_prepare_cb)(unsigned int), 
	return rc >= 0 ? 0 : rc;

}



static void xen_vcpu_setup_restore(int cpu)

static int xen_vcpu_setup_restore(int cpu)

{

	int rc = 0;



	/* Any per_cpu(xen_vcpu) is stale, so reset it */

	xen_vcpu_info_reset(cpu);
@@ -117,8 +119,10 @@ static void xen_vcpu_setup_restore(int cpu) 
	 */

	if (xen_pv_domain() ||

	    (xen_hvm_domain() && cpu_online(cpu))) {

		xen_vcpu_setup(cpu);

		rc = xen_vcpu_setup(cpu);

	}



	return rc;

}



/*
@@ -128,7 +132,7 @@ static void xen_vcpu_setup_restore(int cpu) 
 */

void xen_vcpu_restore(void)

{

	int cpu;

	int cpu, rc;



	for_each_possible_cpu(cpu) {

		bool other_cpu = (cpu != smp_processor_id());
@@ -148,22 +152,25 @@ void xen_vcpu_restore(void) 
		if (xen_pv_domain() || xen_feature(XENFEAT_hvm_safe_pvclock))

			xen_setup_runstate_info(cpu);



		xen_vcpu_setup_restore(cpu);



		if (other_cpu && is_up &&

		rc = xen_vcpu_setup_restore(cpu);

		if (rc)

			pr_emerg_once("vcpu restore failed for cpu=%d err=%d. "

					"System will hang.\n", cpu, rc);

		/*

		 * In case xen_vcpu_setup_restore() fails, do not bring up the

		 * VCPU. This helps us avoid the resulting OOPS when the VCPU

		 * accesses pvclock_vcpu_time via xen_vcpu (which is NULL.)

		 * Note that this does not improve the situation much -- now the

		 * VM hangs instead of OOPSing -- with the VCPUs that did not

		 * fail, spinning in stop_machine(), waiting for the failed

		 * VCPUs to come up.

		 */

		if (other_cpu && is_up && (rc == 0) &&

		    HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL))

			BUG();

	}

}



static void clamp_max_cpus(void)

{

#ifdef CONFIG_SMP

	if (setup_max_cpus > MAX_VIRT_CPUS)

		setup_max_cpus = MAX_VIRT_CPUS;

#endif

}



void xen_vcpu_info_reset(int cpu)

{

	if (xen_vcpu_nr(cpu) < MAX_VIRT_CPUS) {
@@ -175,7 +182,7 @@ void xen_vcpu_info_reset(int cpu) 
	}

}



void xen_vcpu_setup(int cpu)

int xen_vcpu_setup(int cpu)

{

	struct vcpu_register_vcpu_info info;

	int err;
@@ -196,7 +203,7 @@ void xen_vcpu_setup(int cpu) 
	 */

	if (xen_hvm_domain()) {

		if (per_cpu(xen_vcpu, cpu) == &per_cpu(xen_vcpu_info, cpu))

			return;

			return 0;

	}



	if (xen_have_vcpu_info_placement) {
@@ -230,11 +237,10 @@ void xen_vcpu_setup(int cpu) 
		}

	}



	if (!xen_have_vcpu_info_placement) {

		if (cpu >= MAX_VIRT_CPUS)

			clamp_max_cpus();

	if (!xen_have_vcpu_info_placement)

		xen_vcpu_info_reset(cpu);

	}



	return ((per_cpu(xen_vcpu, cpu) == NULL) ? -ENODEV : 0);

}



void xen_reboot(int reason)

arch/x86/xen/enlighten_hvm.c

+5 −4
Original line number Diff line number Diff line
@@ -89,7 +89,7 @@ static void xen_hvm_crash_shutdown(struct pt_regs *regs) 


static int xen_cpu_up_prepare_hvm(unsigned int cpu)

{

	int rc;

	int rc = 0;



	/*

	 * This can happen if CPU was offlined earlier and
@@ -104,7 +104,9 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu) 
		per_cpu(xen_vcpu_id, cpu) = cpu_acpi_id(cpu);

	else

		per_cpu(xen_vcpu_id, cpu) = cpu;

	xen_vcpu_setup(cpu);

	rc = xen_vcpu_setup(cpu);

	if (rc)

		return rc;



	if (xen_have_vector_callback && xen_feature(XENFEAT_hvm_safe_pvclock))

		xen_setup_timer(cpu);
@@ -113,9 +115,8 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu) 
	if (rc) {

		WARN(1, "xen_smp_intr_init() for CPU %d failed: %d\n",

		     cpu, rc);

		return rc;

	}

	return 0;

	return rc;

}



static int xen_cpu_dead_hvm(unsigned int cpu)

arch/x86/xen/enlighten_pv.c

+13 −1
Original line number Diff line number Diff line
@@ -958,7 +958,16 @@ void __ref xen_setup_vcpu_info_placement(void) 
	for_each_possible_cpu(cpu) {

		/* Set up direct vCPU id mapping for PV guests. */

		per_cpu(xen_vcpu_id, cpu) = cpu;

		xen_vcpu_setup(cpu);



		/*

		 * xen_vcpu_setup(cpu) can fail  -- in which case it

		 * falls back to the shared_info version for cpus

		 * where xen_vcpu_nr(cpu) < MAX_VIRT_CPUS.

		 *

		 * xen_cpu_up_prepare_pv() handles the rest by failing

		 * them in hotplug.

		 */

		(void) xen_vcpu_setup(cpu);

	}



	/*
@@ -1432,6 +1441,9 @@ static int xen_cpu_up_prepare_pv(unsigned int cpu) 
{

	int rc;



	if (per_cpu(xen_vcpu, cpu) == NULL)

		return -ENODEV;



	xen_setup_timer(cpu);



	rc = xen_smp_intr_init(cpu);

arch/x86/xen/xen-ops.h

+1 −1
Original line number Diff line number Diff line
@@ -78,7 +78,7 @@ bool xen_vcpu_stolen(int vcpu); 


extern int xen_have_vcpu_info_placement;



void xen_vcpu_setup(int cpu);

int xen_vcpu_setup(int cpu);

void xen_vcpu_info_reset(int cpu);

void xen_setup_vcpu_info_placement(void);

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